[ash-md] Keeps overview mode shield above DesktopBackgroundView

ash/desktop_background/desktop_background_view.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/desktop_background/desktop_background_view.h"
 
 #include "ash/aura/wm_window_aura.h"
 #include "ash/common/display/display_info.h"
 #include "ash/common/session/session_state_delegate.h"
 #include "ash/common/wm/overview/window_selector_controller.h"
@@ skipping 23 matching lines @@
 class LayerControlView : public views::View {
  public:
   explicit LayerControlView(views::View* view) {
     AddChildView(view);
     view->SetPaintToLayer(true);
   }
 
   // Overrides views::View.
   void Layout() override {
     WmWindow* window = WmLookup::Get()->GetWindowForWidget(GetWidget());
+    // Keep |this| at the bottom since there may be other windows on top of the
+    // background view such as an overview mode shield.
+    window->GetParent()->StackChildAtBottom(window);
     display::Display display = window->GetDisplayNearestWindow();
     DisplayInfo info = WmShell::Get()->GetDisplayInfo(display.id());
     float ui_scale = info.GetEffectiveUIScale();
     gfx::Size rounded_size =
         gfx::ScaleToFlooredSize(display.size(), 1.f / ui_scale);
     DCHECK_EQ(1, child_count());
     views::View* child = child_at(0);
     child->SetBounds(0, 0, rounded_size.width(), rounded_size.height());
     gfx::Transform transform;
     // Apply RTL transform explicitly becacuse Views layer code
@@ skipping 175 matching lines @@
   } else {
     // Disable animation if transition to login screen from an empty background.
     desktop_window->SetVisibilityAnimationTransition(::wm::ANIMATE_NONE);
   }
 
   desktop_widget->SetBounds(params.parent->bounds());
   return desktop_widget;
 }
 
 }  // namespace ash